This invention relates to a prosthetic limb including a knee joint, and more particularly to an artificial limb including a single axis knee (knee joint member). More particularly, it is directed to an artificial limb which is so quiet in operating noise that the user sometimes forgets his/her wearing of the artificial limb, and which can provide the perception of comfortableness to the user.
In general, artificial limbs including a knee axis comprises an upper member including a knee plate to which load of the user (amputee) applies, a lower member including a hollow frame extending from the knee portion to the foot portion and connected to the upper member at the knee portion, and a knee axis rotatably supporting the upper and lower members, opposite end portions of the knee axis being supported respectively by a first and a second support member which are provided on the hollow frame. One typical example of this type of prosthetic leg is an above-knee prosthesis which includes a socket supported on an upper end of the knee plate of the upper member and adapted to receive the stump, and a foot member supported on a lower end of the lower member.
There are two types of knee axes for interconnecting the upper and lower members. The first is of a single axis knee (joint) (hereinafter the knee as a joint is simply referred to as "knee" or "knee joint"), and the second is of a polycentric-axes knee (joint) including a plurality of links and variable in the center of rotation in accordance with a bending angle of the knee. The single axis knee joint is simple in construction compared with the polycentric-axes knee joint and can fully endure the dynamic motion of the user as in sports. For this reason, the single axis knee joint is suited to those who need a huge amount of activity.
Because of the construction that the upper and lower members are freely rotatable about the knee axis, it is required for such an artificial limb as including a single axis knee to be designed to generate a proper braking force. As means for generating this braking force, three types were heretofore known. The first type is disclosed by U.S. Pat. No. 3,863,274 (corresponding to Japanese Patent Publication No. 52(1977)-46432 or Japanese Patent Publication No. 57(1982)-41943), in which a braking force is generated by reducing the diameter of a through-hole formed in a brake block. The second type is disclosed by U.S. Pat. No. 4,152,787, in which a braking force is generated by pressing movable discs against stationary discs utilizing the motion of a wedge. The third type is disclosed by U.S. Pat. No. 4,206,519, in which a brake shoe is located inside a hollow brake drum and a braking force is obtained by enlarging the diameter of the brake shoe. Those means of the above-mentioned first to third types are common to each other in the respect that the brake means is a load brake means of a load responsive type in which the braking force generating means are arranged around the knee axis and a braking force thereof is generated by load of the user applied thereto. From a view point of a smaller space required, the first type is the best.
Incidentally, it is required for the single axis knee that the connection around the knee axis or shaft is tightened because load of the user is concentrated on the single knee axis. From this view point, British Laid-Open Patent Publication No. 2,296,442 (corresponding to Japanese Laid-Open Patent Publication No. 8(1996)-229055) discloses an idea that a hollow frame made of a fiber-reinforced plastic is provided on opposite ends thereof with non-circular first and second attaching holes and first and second support members made of metal are cold fitted to the attaching holes, respectively. This British Publication also teaches that a axis is fitted from outside the frame through the first and second support members, and the axis, i.e., knee axis, is fixed by inserting split-pins into opposite end portions of the axis, respectively.
According to the technology disclosed by this British Laid-Open Patent Publication No. 2,296,442 (corresponding to Japanese Laid-Open Patent Publication No. 8(1996)-229055), the first and second support members can be firmly secured to the frame. This arrangement provides the advantage in that a rotation stopper for stopping the rotation when the artificial limb is in a stance phase or swing phase, can be formed integrally with each support member. However, there still remains room for improvement from the view points that play in the axial direction between the brake block around the knee axis and the first and second support members is removed, that play in the rotational direction between the first and second support members and the knee axis, and that play between the member for fixing the knee axis and the frame. The above play appeared to the various places causes a physical contact between adjacent members, thereby generating noises and rubbing which often provide the perception of uncomfortableness to the user.
As one attempt for removing play in the axial direction of the knee axis, there can be contemplated a method for providing a spacer between the support members on the frame side and the brake block. However, it became known that this spacer is subjected to wear caused by the relative rubbing motion generated between the support members or the brake block and the surface of the spacer facing those support members or brake block. The reason is that the spacer rotates together with the knee axis. The wear of the spacer results in generation of play (chattering) in the axial direction. In addition, there is a possibility that the frictional powders produced by wear invade into the interior of the brake block to degrade the braking performance. The problems mentioned above are not only inherent in the first type load brake means but also in the second or third type means.